Quark has released an El Capitan Update for QuarkXPress 2015, providing full OS X 10.11 support. They also published this to their Press Center “Quark does not intend to provide support for running El Capitan on versions of QuarkXPress prior to QuarkXPress 2015.” http://www.quark.com/About_Quark/Press/PressDetail.aspx?ncid=2141